Nitration reactions are important chemical transformations employed in the production of many energetic materials. For example, a conventional method for manufacturing the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) uses 1,3,5-tricholorobenzene (TCB) as a starting material in a two stage process that includes: (1) a nitration reaction; and (2) an amination reaction. However, due to the environmental hazards associated with halogenated aromatics, phenolic compounds are, when applicable, substituted as starting materials in these types of syntheses. Unfortunately, nitration of even moderately activated aromatics may result in vigorously exothermic reactions that require strict temperature control by way of substantial cooling. Such processing requirements may be difficult to maintain, particularly in terms of scaling-up nitration reactions to production level quantities.
Conventional methods of producing nitro phenols, therefore, avoid the direct nitration of the phenol and employ processes that initially form an intermediate compound that may then be nitrated. Phenol, for instance, is first sulfonated to form a mixture of phenolsulfonic acids that are then nitrated to produce picric acid (2,4,6-trinitrophenol). Resorcinol is reacted similarly to produce styphnic acid (2,4,6-trinitroresorcinol), and phloroglucinol (1,3,5-trihydroxybenzene) is first converted to a triacetoxy derivative, which is nitrated and then hydrolyzed to produce trinitrophloroglucinol. Another method of preparing nitrophenols is by hydrolysis of an appropriate halogenated derivative. For example, 2,4-dinitrochlorobenzene may be hydrolyzed by aqueous alkali to form 2,4-dinitrophenol, which may be subsequently nitrated to picric acid. Similarly, 1,3,5-tribromo-2,4,6-trinitrobenzene may be hydrolyzed to produce trinitrophloroglucinol. These processes do not offer significant advantages in time and labor, and the presence of halides is still problematic. Furthermore, the action of the alkali on the nitro groups may introduce unwanted decomposition products that may result in impure products.
Bellamy et al., Propellants, Explosives, Pyrotechnics, 27: 49-58 (2002), disclose a three-stage route to manufacturing TATB using 1,3,5-trihydroxybenzene as a starting material. The 1,3,5-trihydroxybenzene is nitrated using dinitrogen pentoxide (N2O5) in sulfuric acid (H2SO4), or a mixed acid nitration of the triacetate analog.
Bellamy et al., J. Chem. Research, 2002(9): 412-413 (2002), disclose a process for nitrating 1,3,5-trimethoxybenzene using dinitrogen pentoxide dissolved in an organic solvent, such as dichloromethane or acetonitrile, in the presence of nitric acid or sulfuric acid. In all experiments where an amount of dinitrogen pentoxide sufficient to convert 1,3,5-trimethoxybenzene to the tri-nitro derivative was used, the product yield was 22-65%. The highest conversion of 1,3,5-trimethoxybenzene into 1,3,5-trimethoxy-2,4,6-trinitrobenzene was achieved when sulfuric acid was present. However, Bellamy et al. observed that too much sulfuric acid caused the yield to be drastically reduced. Additionally, the nitration process using nitric acid was observed to cause significant side-reactions.
DeFusco et al., Organic Preparations and Procedures International, 14(6): 393-424 (1982), disclose a preparation of trinitrophloroglucinol performed by adding a nitric acid-sulfuric acid mixture to a phloroglucinol-sulfuric acid mixture. The preparation produced yields of up to 70%.
M. P. Majumdar and N. A. Kudav, Ind. J. Chem., 14B:1012-1013 (1976), disclose nitration of aromatic compounds, such as anisole, diphenyloxide, methyl benzoate, and acetophenone, with urea nitrate-sulfuric acid. A mixture of the aromatic compound and concentrated sulfuric acid is treated with urea nitrate at 0° C. to 10° C. while stirring for one hour to achieve nitration.
Organic Chemistry of Explosives, by J. P. Agrawal and R. D. Hodgson, pp. 142-143, discloses a nitration process using a solution of potassium nitrate in sulfuric acid to nitrate o- or p-acetanilide to form picramide. Metal nitrates are also disclosed for use with Lewis acids for aromatic nitration, as well as using alkyl nitrates in the presence of sulfuric acid and Lewis acids, such as SnCl4, AlCl3, or BF3.
U.S. Pat. No. 4,032,377 to Theodore M. Benziger discloses a method for producing TATB from TCB using a nitration process, followed by an amination process. The TCB is nitrated using a mixture of oleum and sodium nitrate at 150° C. for 4 hours to form 1,3,5-trichloro-2,4,6-trinitrobenzene, which is, in turn, aminated using ammonia in toluene at 150° C. This process relies on extreme reaction conditions that necessitate high temperatures over relatively long periods of time. Additionally, environmental concerns have arisen over the release and use of halogenated aromatic compounds, such as TCB, in the manufacture of TATB, and subsequent disposal of such compounds. Halogenated aromatics, and other halogen-containing compounds, have been found to be highly toxic, potential carcinogens. Accordingly, unconverted halogenated compounds and halogen containing side-products must be suitably disposed of to prevent pollution which, in turn, results in increased manufacturing costs.
U.S. Pat. No. 4,952,733 to Ott and Benziger discloses a method of preparing TATB from nitration of 3,5-dichloroanisole. The reaction sequence consists of a two step process involving a nitration reaction, followed by an amination reaction. The nitration reaction is performed by adding 3,5-dichloroanisole to a mixture of nitric acid and sulfuric acid at a temperature of 100° C.